The invention relates to a method for plasma treatment of workpieces in which the workpiece is placed in a plasma chamber, and in which, subsequently, under the influence of negative pressure after the ignition of plasma, a coating is precipitated on the workpiece, and in which the process sequence is optically monitored at least temporarily.
Moreover, the invention also relates to a device for plasma treatment of workpieces which has at least one evacuatable plasma chamber for receiving the workpieces, and in which the plasma chamber is arranged in the area of a treatment station, and in which the plasma chamber is defined by a chamber floor, a chamber cover as well as a lateral chamber wall, and in which the plasma chamber is coupled to a device for the optimum monitoring of a process sequence.
Such methods and devices are used, for example, for providing synthetic materials with surface coatings. In particular, also already known are devices of this type for coating inner and outer surfaces of containers which are intended for packaging liquids. Moreover, devices for plasma sterilization are known.
PCT/WO 95/22413 describes a plasma chamber for the internal coating of bottles of PET. The bottles to be coated are lifted through a movable bottom into a plasma chamber and are connected to an adapter in the area of a bottle opening. An evacuation of the bottle interior can be effected through the adapter. Moreover, a hollow gas lance is introduced into the interior of the bottles in order to supply process gas. An ignition of the plasma takes place with the use of a microwave.
It is also known from this publication to arrange a plurality of plasma chambers on a rotating wheel. This supports a high production rate of bottles per unit of time.
In EP-OS 10 10 773 a supply device is explained for evacuating the interior of the bottle and supplying process gas. PCT-WO 01/31680 describes a plasma chamber into which the bottles are inserted by a movable cover which previously had been connected to the mouth portion of the bottles.
PCT-WO 00/58631 also already shows the arrangement of plasma stations on a rotating wheel and describes for such an arrangement an assignment of negative pressure pumps and plasma stations in groups, in order to support a favorable evacuation of the chambers as well as the inner spaces of the bottles. Moreover, the coating of several containers in a common plasma station or a common cavity is mentioned.
Another arrangement for carrying out an internal coating of bottles is described in PCT-WO 99/17334. In this case, especially an arrangement of a microwave generator above the plasma chamber, as well as a vacuum and operation medium through a bottom of the plasma chamber, is described.
In DE 10 2004 020 185 A1 a gas lance is already described which can be moved into the interior of a preform to be coated and for supplying process gas. The gas lance can be positioned in the longitudinal direction of the container.
In a predominant number of the known devices, container layers of silicone oxides produced by the plasma having the general chemical formula SiOx are used for improving the barrier properties of the thermoplastic material. Such barrier layers prevent a penetration of oxygen into the packaged liquids, as well as a discharge of carbon dioxide in the case of CO2 containing liquids.
Because of the chemical elements contained in the plasma, the plasma has characteristic spectral lines. Therefore, an optical monitoring for carrying out a plasma coating is already described in U.S. Pat. No. 6,117,243. In this case, the evaluation of the radiation emission is carried out within the range of a wave length of 425 nanometers.
EP 1 948 846 explains another method for monitoring a plasma coating. In that case, an evaluation in a spectral range of 800 nanometers to 950 nanometers takes place. An evaluation of a difference between signals of a first band width as the reference and the signals of a second band width takes place.
The previously known methods and devices are not yet sufficiently suitable for making available a process monitoring which is reliable, on the one hand, as well as a process monitoring which is robust with respect to changing border conditions.